S4 battery complete discharge

I have a galaxy S4 that I have not been using since I got an S6. The phone was off for a long time and now when I'm powering on the phone, it is not turning on. Once it happened and I had to charge it for a while before it started charging at 0% but now it is not charging at all. The phone did not have any battery issues prior to this.
Is the battery dead or completely discharged and what should be done other than replacing the battery?

Thanks